Let soil temperature guide you when planting vegetables
March 30, 2023 | View PDF
Weeks of cold temperatures and rain have unsettled the gardening season. You may be raring to get your garden – but hold. Sowing seeds or planting seedlings at the wrong time will bring nothing but heartache.
“One of the biggest mistakes people make is to plant too early,” said Weston Miller, a former horticulturist with the Oregon State University Extension Service. “They get excited when it’s sunny for a few days, put plants in the ground, and think they will grow. But the seeds either rot from damping off fungus or germinate very slowly. At the very least, they’ll be stressed for the rest of the season and never catch up.”
Right about now in the Willamette Valley is usually when you can get away with planting cool-season vegetables like peas, arugula, mustard, radish, and turnip in prepared planting beds. Also, carrots, beets, scallions, chives, parsley, and cutting greens that are easy to grow from seed; or plant already started transplants of kale, head lettuce, chard, leeks, and onions.
This year, however, paying attention to soil temperature is the best way to go. An inexpensive soil thermometer helps keep planting time in perspective.
“Fifty degrees is a good benchmark for cool-season crops,” Weston said. “And the soil should be 60 degrees or more for warm-weather plants like tomatoes, peppers, and basil. In fact, for tomatoes it should ideally be 65 to 70.”
If you can’t resist the urge to plant warm-season vegetables before the soil warms sufficiently, Miller recommends using some sort of protection from the chill like a floating row cover, individual glass or plastic cloches or even milk jugs or soda bottles with the top cut-out and turned upside down over plants. For directions on building a large, greenhouse-type cloche with PVC pipe and plastic, check out the OSU Extension guide on “How to Build Your Own Raised Bed Cloche.”
“Gardening depends on the weather, which is unpredictable,” Miller said. “But it pays to wait.”
You’ll find more information about vegetable gardening, including schedules for planting 45 vegetables in all regions of Oregon, in the comprehensive Extension publication called “Growing Your Own.” You’ll also find information on how far apart to space plants and how much to grow for a family of four.
Weston Miller’s top five tips for a successful vegetable garden
Prepare the soil. Before planting, add a moderate amount of compost (¼- to 1-inch) and a balanced fertilizer (all three numbers on the bag are the same) according to package directions. Incorporate the materials into the top 8 to 12 inches with a digging fork or spade. Rake bed before planting seeds or transplants. For new garden beds: Remove sod or weeds to expose soil. Liberally add 4 to 6 inches of compost, agricultural lime, and a balanced fertilizer and incorporate into the top 8 to 12 inches with a digging fork or spade. Prepare a seed or transplant bed with a rake. Next fall, add 5 to 10 pounds per 100 square feet of lime to beds.
In addition to adding complete fertilizer to the soil, use a soluble fertilizer like fish emulsion for transplants, especially early in the season or if the plants are not thriving.
Use transplants when possible. Crops that do best when seeded directly into the garden include carrots, parsnips, beets, radishes, turnips, mustard, and arugula. Most other crops can and should be transplanted to make the gardening process easier, particularly for weed control. Grow your own transplants or look for high-quality starts (not root bound, stunted, or off-color) at the garden center for the best results.
Control weeds early in the growth cycle of your veggies. Plan to weed your veggie beds at least once per week for the first four weeks of the plant’s growth to get the edge on this ongoing challenge in the garden.
Monitor and control slugs and other insect pests, often. Keep an eye out for slugs. You can find them under debris and in the folds of plants and dispatch them by dropping them into soapy water. Look for aphids, imported cabbage butterfly larvae, and other critters on the underside of the leaves. Squash them!